Breast cancer is the most commonly diagnosed female malignancy in the United States. Angiogenesis plays a critical role in tumorigenesis and metastasis in breast cancer. Thus, antiangiogenic therapies, either as monotherapy or in combination with other therapies are promising and being intensely investigated in both preclinical and clinical studies. The goal of the proposed project is to test novel endogenous antiangiogenic peptides in mouse models of human breast cancer. We will test peptides identified in our laboratory derived from three classes of proteins: thrombospondin type I repeat-containing proteins;CXC chemokines;and alpha5 fibrils of collagen type IV. We have performed careful in vitro screening of the identified peptides using endothelial cell proliferation and migration assays, and demonstrated activity in several in vivo assays in mice including subcutaneous basement-membrane-extract plugs, corneal micropocket, and tumor xenografts. Based on these studies, we have narrowed the selection to three leading peptides. We hypothesize that the identified peptides inhibit tumor angiogenesis in breast cancer and can therefore inhibit or significantly reduce the tumor growth. To test this hypothesis, we will examine antiangiogenic properties of the selected peptides using a mouse model of human breast cancer. Two human breast cancer cell lines, the less invasive MCF-7 and the more invasive MDA-MB-231, will be used to form orthotopic tumor xenografts in severe immune deficient (SCID) mice. The peptides will be administered intraperitoneally (i.p.) and tumor size will be monitored. In addition to naked peptides, peptides encapsulated into polymer nanomicelles will be used to increase their solubility, half-life, and enhance systemic administration. Tumor blood volume and vascular permeability will be monitored non-invasively using Magnetic Resonance Imaging (MRI). Immunohistochemistry will be performed to determine the effects on the vasculature and on the cancer and stromal cells. We have identified a number of peptide receptors on the endothelial cells in vitro using receptor neutralization by monoclonal antibodies. Specifically, we have identified receptors CD36, CD47, CXCR3, and beta-1 and beta-3 integrins. We will conduct studies on the expression of these receptors in tumor xenografts. We will also conduct pilot studies where we will apply the peptides in combination with other antiangiogenic agents (e.g., agents interfering with the VEGF pathways) and chemotherapeutic agents to test whether their action is additive or synergistic and if they can provide added therapeutic benefits. The proposed development of novel antiangiogenic agents would have a significant impact on research in tumor angiogenesis and other diseases associated with neovascularization. PUBLIC HEALTH RELEVANCE: Breast cancer is the most commonly diagnosed female malignancy in the United States. Approximately 180,000 new cases of invasive breast cancer have been diagnosed in 2007. The relevance of this research to public health is that the work may lead to identification of new antiangiogenic agents (inhibiting abnormal blood vessel growth) for the treatment of breast cancer and potentially other forms of cancer. It will also provide a better understanding of the role of several tissue proteins in maintaining healthy vascular balance and how this role may change in disease conditions.